Mammography is the process of obtaining x-ray images of the human breast for diagnosis or surgery. It involves positioning a patient's breast in a desired orientation against a cassette holder of a mammography unit (also known as a “bucky”), compressing the breast with a compression device, and then exposing the breast to x-rays to create a latent image of the breast on an image receptor. After exposure, the compression device is released. The image receptor is usually a film in contact with an intensifying screen contained within a cassette. The cassette is inserted into a cassette holder before every image is taken and removed after every image. The film is removed from the cassette and developed to produce a radiographic image of the breast.
A complete mammographic study usually involves at least two x-ray exposures of each breast. One exposure is a craniocaudal view in which the breast is compressed in a superior-inferior direction, i.e., from the direction of the patient's head downward, against a tube-side surface of the cassette holder. The plane of the tube-side surface of the cassette holder is parallel to the floor and the x-ray beam is directed vertically downward. A second exposure is a lateral or oblique view in which the breast is compressed mediolaterally, i.e., from the direction of the patient's midline sidewise, against the tube-side surface of the cassette holder which is angled, along with the axis of the x-ray beam, relative to the floor.
The compression device includes a rectangular flat plate, called a compression paddle or a compression plate, which is attached to the mammography unit between an x-ray tube assembly and the cassette holder. The edges of the paddle or plate are turned upward away from the cassette holder to provide a smooth curved surface for patient comfort. The compression paddle is usually made of thin, light-transparent, plastic that absorbs only a small fraction of the incident x-ray beam. The compression paddle is moved either manually or by power drive to apply a compression force to the breast, thereby flattening the breast against the cassette holder to a near uniform thickness. U.S. Pat. No. 6,049,583 issued to the present inventor discusses methods and apparatus for measuring compression force in mammography. After x-ray exposure, the compression force is released for patient comfort.
To properly position the patient's breast in a desired orientation, a technologist is guided by a light beam originating from the x-ray tube assembly that passes through a collimator and the compression paddle and illuminates the area of the cassette holder that will be exposed to x-rays, i.e., the imaging area. As is well known in the field, to properly position the breast, the patient's chest wall or other regions of the body, depending on the desired view, are brought into tight contact with the rigid surfaces of the cassette holder, its edges, and corners. This procedure has the effect of forcing the patent's anatomy to contour to the shape of the cassette holder, which often causes patient discomfort and pain.
Oftentimes, overlapping internal structures are present within the breast tissue that can obscure their delineation in a radiographic image. As a result, it is often necessary to reposition the breast slightly in order to arrive at a diagnosis. This requires repositioning the patient for each view with the attendant discomfort.
During positioning, compressing, and imaging, parts of the patient's body come into contact with the cassette holder. The cassette holder is a rectangular, box-like device that has a flat tube-side surface against which the breast is compressed, a flat outer surface along one edge of the tube-side surface which contacts the patient's chest wall or torso, and two flat side surfaces opposite each other along the other edges that can come into contact with other parts of the patient's anatomy such as the underarm and axilla. Each of the side surfaces has an opening, typically rectangular, to a cassette tunnel. The openings are used for insertion and removal of the cassette. The tube-side surface includes an imaging area, which is transparent to x-rays, located directly above the cassette as it resides in the cassette holder, and where the breast is positioned during imaging, and a solid section which is not transparent to x-rays. Within the cassette holder is an antiscatter grid assembly. The cassette holder is held in position on the x-ray unit by slidably engaging to a support member. Because the surfaces of the cassette holder may come into contact with blood or other infectious material, they must be able to withstand contact with the chemical agents usually used for disinfecting purposes. Cassette holders come in different sizes depending on the size film to be used.
In U.S. Pat. No. 5,541,972 by Anthony, disposable sanitary cushioning strips that are attached to the outside of the cassette holder are described. The strips are intended to be replaced between patients. The strips are placed to provide cushioning only along the outer surface of the cassette holder, and its edges and corners, where the patient's torso contacts the cassette holder. The Anthony invention, therefore, provides only limited relief for the patient since it does not cushion the breast from contact with the tube-side surface of the cassette holder.
Others in the art use a radiolucent pad, the MammoPad®, supplied by BioLucent, Inc., that is placed on the tube-side surface of the cassette holder and is folded over to the outer surface of the cassette holder facing the patient's torso. The pad is held in position by a peel-off layer of adhesive that covers the underside. This device, however, does not cushion the underarm or axilla areas for mediolateral or lateral views unless it is removed and repositioned. Moreover, if it is repositioned for these views, it blocks access to an opening to the cassette tunnel. In addition, a new pad is used for each patient, and many mammography facilities find the cost per pad to be prohibitive under current third party reimbursement schedules.
In U.S. Pat. No. 5,311,883 to Sherman, a sanitary shield for dedicated mammography apparatus is discussed. According to Sherman, the shields are made using known vacuum molding techniques. Therefore, although the shields may be flexible to a certain extent, they are not compressible and would not provide cushioning or reduction of discomfort to a patient.
In U.S. Pat. No. 5,479,927 to Shmulewitz, a gel pad that can be used in conjunction with conventional mammography equipment is discussed. The gel pad is located on the underside of a compression plate and fails to cushion the breast from either the tube-side surface or the outer surface of the cassette holder.
There remains a great need for comfort devices for use during mammography which can minimize or eliminate the pain and discomfort experienced by the patient. To be useful in clinical practice such devices must also not add significantly to the cost of the examination.